9) Zigzag lines stitched from corner in varying lengths, smallest setting creating random dark patches.
10) Zigzag variant increasing stitch length applied more freely diagonally across the square.
11) As above, but less densely applied.
12) Decorative stitch varying length and as a result lines are closer together.
On a purely practical note the dense stitching on sample 12 was least successful: the fabric is scrumpled up and frayed so it has not been possible to layer the stitching as much as hoped for. If I used this idea I'd make a larger sample and cut out the required amount.
Sample 10 achieves layers of stitch, contrasts in zig-zag length and small blocks of dark stitching.
Sample 9, though very simple in execution, manages to achieve patches of darker and lighter fabric reminiscent of the 3D effect of ripples on water.